A major revolution in video display technology includes flat screens based on either liquid crystal display (LCD) or plasma display panel (PDP) technology that are rapidly replacing the cathode ray tube (CRT) technology that served as the primary display device for more than a half a century. A significant consequence of the new video display technologies is that pictures may now be displayed at higher picture-rates with progressive scanning on a flat screen. The new video display technologies may also facilitate a faster transition from standard definition television (SDTV) to high-definition television (HDTV). However, legacy video compression systems still use formats with lower picture-rates and may be unable to optimally display legacy video on modern display screens.
An artifact known as “motion judder” may occur when the picture rate of a video sequence is excessively low. Motion judder may occur when the temporal sampling rate is too low to describe motion in a scene. The objects in input pictures may be shifted on either side of a required output picture. A temporal digital filter interpolation method may be used to determine pixel intensity values. The signals describing motion of each of the objects within a scene may be referred to as motion vectors. Each pixel or region with the same movement may be allocated a motion vector. The motion estimation system may determine these motion vectors and failing to find a correct motion vector and/or misusing the motion vector in a picture rate converter may lead to noticeable artifacts. When large camera movements occur, regions of a picture close to the borders may have significantly less reliable motion vectors than those closer to the middle and special processing may be required at the picture boundaries.
Telecine is a process that may be used to transfer film sequences to television. Telecine may involve a vertical low-pass Kell-factor filtering of a source image followed by a frame-rate conversion through field repetition. For NTSC, the first 3 fields may be received from the first film frame, followed by 2 fields from the second film frame, followed by 3 fields from the third film frame and so on. The non-uniformity of frames may cause motion judder. In cases where the telecine transfer maps the same number of fields to a single frame, a blurring or stuttering phenomenon may be present because of low temporal resolution of the source images and the near-simultaneous display of two temporally-disparate images.
Interlaced video comprises of fields, each of which may be captured at a distinct time interval. A pair of fields, for example, a top field and a bottom field may be considered to comprise a frame. The pictures forming the video comprise a plurality of ordered lines. During one of the time intervals, video content for the even-numbered lines may be captured. During the other time interval, video content for the odd-numbered lines may be captured. The even-numbered lines may be collectively known as the top field, while the odd-numbered lines may be collectively known as the bottom field. Alternately, the odd-numbered lines may be collectively known as the top field, while the even-numbered lines may be collectively known as the bottom field.
In the case of progressive video frames, all the lines of the frame may be captured during one time interval. Interlaced video may comprise fields that were converted from progressive frames. For example, a progressive frame may be converted into two interlaced fields by organizing the even numbered lines into one field and the odd numbered lines into another field.
When encoding frame pictures, an encoder may utilize coding methods that treat frames as progressive video. These are generally referred to as progressive coding tools. It may be desirable to make the optimum choice between field and frame coding for every field or every pair of fields. The 3:2 pulldown video may comprise a pattern wherein some fields from the original content may be repeated two fields after their first occurrence, forming TBT (top bottom top) or BTB (bottom top bottom) patterns. When encoding video comprising a 3:2 pulldown pattern, it may be desirable to detect and reverse the 3:2 pulldown pattern to reconstruct the video, for example, 24 frames per second progressive video before encoding, and to encode the resulting frames of video using progressive coding tools.
Traditional 3:2 pulldown detectors measure the similarity of fields of the same polarity, for example, top (T) and T or bottom (B) and B, two fields apart, and may utilize this similarity measure to decide whether the current video input follows a 3:2 pulldown pattern or not. In 3:2 pulldown, the first and third fields of the TBT and BTB frames are theoretically identical, although they may be affected by noise.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.